Can someone explain this to me?

My husband recently took a job driving for Hess (in Charleston, SC), delivering gas. He's required to work 60 hours a week, but they don't pay over time until you go over 60 hours ... however, you're not allowed to work over 60 hours (if you do you get 'suspended' and so does the dispatcher who was on duty at the time).

I didn't get it ... how can they not pay overtime? So I called the SC Labor Board and they say it's because their drivers may cross state lines. My husband has only been there for 3 months but he's never crossed state lines, nor has anyone else from his terminal. But I guess the possibility is there.

But what does that have to do with anything? I just don't understand it. Does anyone know why this is?

Thanks in advance.